Accurately advancing paper between print swaths is becoming a greater and greater challenge. In early inkjet printers, the swath advances were short and the allowable error large. With the push to improve print quality and speed, the swath advances are getting larger and at the same time the accuracy needs to be greater. This invention provides accurate pen/paper positioning regardless of the length of swath advance.
Early inkjet printers relied on stepper motor position through a gear train to a drive shaft with rubber wheels to position the paper. This was adequate for the small advances and the coarse large dots. Subsequent improvements in swath advances have been accomplished using higher precision gears, micro-stepping, and drive rollers with lower run-out.
More recently an encoder has been added to the drive roller shaft to get direct feedback of drive shaft and reduce the requirement for precision gears. A second encoder is typically needed to compensate for eccentricity of the encoder disk. In addition, the manufacturing variation in the drive tire diameter may require a calibration routine to measure the drive tire circumference. This information is stored in non-volatile RAM and used to further improve the swath advance accuracy.
All these improvements have helped to meet the requirements for each new generation of printer. With the precision required for the next generation products, the existing technologies are again exceeded.
The swath advance distances can be expected to increase substantially. At the same time the number of dots per inch is increasing, e.g. from 600 dpi to 1200 dpi. In the past, system paper swath advance accuracies on the order of ½ to ¼ dot row have been required. To position paper to +/− 0.0002 inches for paper advances greater than one inch would be difficult to achieve using conventional techniques.